BALTIMORE -- A pair of trades the Orioles made on Saturday changed the team's needs ahead of September callups, but there are still some spots that can be filled, and the O's will begin the process of expanding their roster on Monday.

Manager Buck Showalter said the Orioles will add a pair of pitchers on Monday and bring in two position players, including catcher Steve Clevenger, on Tuesday. Clevenger was optioned to Class A Short-Season Aberdeen on Sunday to make room for Wei-Yin Chen to be recalled from the Gulf Coast League Orioles ahead of his start. Once Aberdeen's season ends on Sunday, Baltimore can recall Clevenger without waiting the usual 10 days.

Relief pitcher Ryan Webb will likely be one of the arms added, and starting pitcher-turned-reliever Joe Saunders is a candidate to be the other. Webb played most of the season with the O's before being sent to Triple-A Norfolk when Baltimore acquired relief pitcher Andrew Miller at the Trade Deadline. He posted a 3.80 ERA in 42 appearances with the O's.

Saunders, who was released by both the Rangers and Royals this season, signed with the Orioles on Aug. 5 and has a 1.50 ERA in 10 appearances for Norfolk. He started for Baltimore in the American League Card Game against the Rangers in 2012.

The O's will have to add Saunders to the 40-man roster before activating him. There's currently one open spot on the roster, and another could become available if the Orioles move injured third baseman Manny Machado to the 60-day disabled list.

Relief pitcher Preston Guilmet, who is on the 40-man roster, is also a possibility to be added for his seventh stint in the Majors this season.

"We have plenty of room," Showalter said.

Baltimore will also activate pitcher Kevin Gausman ahead of Monday's game to make his scheduled start.

A day later, after all Minor League seasons have finished, the O's will add some bats. Clevenger will come back, and the Orioles will bring some depth with him. Catcher Mike Ohlman, second baseman and outfielder Steve Lombardozzi, and designated hitter Henry Urrutia are the remaining position players on the 40-man roster. Cord Phelps, Quintin Berry, Dariel Alvarez and Christian Walker are among the non-roster candidates to be added in September.

Those that aren't added could head to Sarasota, Fla. Showalter said about 10 players will head down there to be part of Baltimore's September taxi squad